1. Technical Field
The present invention relates to a motor control strategy of an electric shift-by-wire (SBW) system and, more particularly, to a method of performing pulse width modulation (PWM) waveform simulation control in order to solve a problem in that an impact/noise occurs in a motor control process.
2. Description of the Related Art
A transmission is a core element in the driving of a vehicle that functions to transfer electric power, generated by an engine, to the wheels by increasing or decreasing rotatory power of the engine based on a driving condition of the vehicle.
The transmission is divided into a manual transmission and an automatic transmission depending on a gear shifting method. The automatic transmission is recently used in most of vehicles due to an advantage in that convenient and smooth driving is possible because a separate clutch manipulation is not necessary.
The automatic transmission is divided into an automatic transmission equipped with a mechanical SBW system for performing gear shifting using a mechanical link structure through a wire and an automatic transmission equipped with an electric SBW system for performing gear shifting using an electrical signal using a substrate instead of the mechanical link structure.
The electric SBW system has an advantage in that an impact and vibration are significantly reduced compared to a conventional mechanical SBW system because it can transfer information of a transmission stage selected by a driver as an electrical signal without a mechanical connection between the transmission and a shift lever unlike the mechanical SBW system despite a disadvantage of a high price. Vehicles recently adopting an electric SBW system owing to such an advantage are gradually increasing.
In the electric SBW system, a gear shifting part includes a detent plate chiefly rotatably driven by an electric motor, a manual valve positioned in the detent plate to operate in conjunction with the detent plate and to set a shift range of the automatic transmission as a shift range corresponding to the rotation position of the detent plate, and a detent spring inserted into a concave part formed in the detent plate to regulate the rotation of the detent plate, to restrict the shift range within a specific range, and to have supportable regulation means.
However, the electric SBW system does not completely prevent the occurrence of an impact and vibration because it rotatably drives an electric actuator, that is, an electric motor.
FIG. 9 is a diagram showing the state in which a motor position according to a conventional technology is controlled.
Referring to FIG. 9, the motor may be accelerated by a shape of the detent plate and elastic repulsive power of the detent spring. The accelerated motor generates an impact and noise in a process for the end of the detent spring to be engaged with the detent plate, and may deteriorate durability because the motor generates heat when it is used for a long period of time.
In a conventional electric SBW system, in order to reduce an impact and noise occurring in this process, for example, a control strategy is used in which when 90% of a target position (e.g., concave part) is reached, the motor is controlled to be held for a given time (e.g., 100 ms) and motor driving becomes OFF.
It is however difficult to satisfy the requirements of a low vibration characteristic and silence for a vehicle despite such efforts to reduce an impact and noise.